Transcobalamin II (TC II) is known to carry vitamin B-12 (B-12) in both early and late stages of plasma transport. The congenital absence of TC II is incompatible with life unless the subject receives enormous amounts of parenteral B-12. The objective of the proposal is to determine how TC II promotes the uptake of B-12 and how does TC II fit into the overall transport process. One part of the study will be to purify TC II and make an anti TC II. The antibody will be used to evaluate this uptake process and the localization of TC II in tissues. The uptake process will be studied in canine organs in perfusion. Evaluation will include a search for membrane receptors, the need for TC II by different tissues, the synthesis of TC II and the fate of TC II-B-12 within the cell.